Cdkn2a/p16INK4A Loss Impairs Spatial Memory in Young Adult Mice Independently of Alzheimer ’s-Associated Genetic Pathways

The cyclin-dependent kinase inhibitor CDKN2A/p16INK4A is a central regulator of cellular senescence, widely studied in ageing and cancer. Although its expression increases with age and disease, its role in the adult brain remains poorly defined. Recent evidence suggests a possible contribution to neuroinflammation and cognitive decline in Alzheimer’s disease (AD), but underlying mechanisms are unclear. We investigated the functional impact of p16INK4A inactivation on spatial cognition and hippocampal gene expression in adult mice under normal and amyloidogenic conditions using the AppNL-G-F AD model. Loss of p16INK4A led to mild but consistent impairments in spatial learning and memory retrieval, without exacerbating early deficits in AppNL-G-F mice. Hippocampal transcriptomic analysis revealed that p16INK4AKO upregulated metabolic, mitochondrial, and translational pathways, while downregulating synaptic and cytoskeletal genes. In contrast, AppNL-G-F mice displayed strong immune activation. The double mutants showed additive transcriptional changes, yet GSEA indicated non-linear interactions in synaptic and immune-related pathways. Unexpectedly, p16INK4A deletion alone enriched senescence-associated signatures, despite the loss of this canonical senescence gene. Constitutive p16INK4A loss impairs spatial memory and causes broad transcriptomic remodelling in the adult hippocampus, independently of amyloid pathology. These findings uncover non-canonical roles for p16INK4A in neuronal homeostasis and emphasise the need for temporally controlled models to better dissect the brain-specific functions of senescence regulators in ageing and neurodegeneration.